It's not clear when Lugoj died, but by the end of the confrontation in the Sernog Monastery he was subdued by the progenitor of his bloodline, being impaled on a massive wooden hook and hidden through a powerful invisibility spell. The Tzimisce Antediluvian then fleshcrafted into a facsimile of Lugoj and proceeded to fake his own Diablerie, successfully fooling the anarchs into thinking that he was dead and that the real Lugoj had prevailed.

The ancient went to torpor after he took over the identity of Lugoj and resurfaced in a new form in the Final Nights.[1]